Hi Akihiko,
On Mon, 20 Jul 2026 at 06:39, Akihiko Odaki
<[email protected]> wrote:
...
> +/**
> + * kvm_pmu_create_perf_event - create a perf event for a counter
> + * @pmc: Counter context
> + */
> +static void kvm_pmu_create_perf_event(struct kvm_pmc *pmc)
> +{
> + struct kvm_vcpu *vcpu = kvm_pmc_to_vcpu(pmc);
> + struct arm_pmu *arm_pmu = vcpu->kvm->arch.arm_pmu;
> +
> + if (kvm_pmu_fixed_counters_only(vcpu->kvm)) {
> + do {
> + arm_pmu = kvm_pmu_probe_armpmu(READ_ONCE(vcpu->cpu));
> +
> + if (!arm_pmu) {
> + pr_warn_once("kvm: Unsupported PMU variation
> detected.\n");
> + add_taint(TAINT_CPU_OUT_OF_SPEC,
> LOCKDEP_STILL_OK);
> + return;
> + }
Sashiko flagged that this can leave the perf event out of sync with
the sysreg, which looks plausible: on a pCPU with no registered pPMU
this returns without recreating the event, so a guest event-type
change there updates the sysreg but not the event, and after migrating
back to a pCPU the original pPMU covers, kvm_pmc_enable_perf_event()
re-enables the stale event instead of recreating it.
I know you treat the no-pPMU case as out of spec, but the dropped
update lands once the vCPU is back on a normal pCPU. Is this intended?
Cheers,
/fuad
